THE SUBCLASS DIAPSIDA 281 



anterior part of the skull of this genus is poorly known, and its im- 

 mediate relationships with the other genera are still in doubt. 



Upper Triassic. Rhynchosaurus Owen, England. Hyperodapedon 

 Huxley, Scotland, India. Stenometopon Boulenger, Scotland. 

 Howesia Broom, South Africa. 



B. Suborder Sphenodontia (Rhynchocephalia vera) 



Upper temporal opening bounded by parietal, squamosal, post- 

 frontal, and postorbital. A single row of acrodont teeth on maxillae, 

 dentaries, and palatines. Premaxillae with a decurved beak, usually 

 with teeth. Frontals and parietals paired. No lacrimals. A parietal 

 foramen. Humerus with an entepicondylar foramen, sometimes 

 also with an ectepicondylar foramen. Pelvis with large pubo-ischiatic 

 vacuity. Carpus primitive. Twenty-three to twenty-five presacral 

 vertebrae, the neck with not more than eight. Parasternal ribs 

 present. 



Two genera only, the living Sphenodon and the Jurassic Homoeo- 

 saurus, can be located with certainty in this suborder. Sphenodon 

 has long enjoyed the reputation of being the most primitive of living 

 reptiles, as evidenced by the persistent dorsal intercentra, deeply 

 amphicoelous vertebrae, and the single-headed ribs of primitive 

 type. So far as known Homoeosaurus agrees closely, except that it 

 has no uncinate process on the ribs, a character in which Spheno- 

 don is almost unique among reptiles. Probably it has dorsal inter- 

 centra, but this remains to be determined. It has also no ectepi- 

 condylar foramen present in Sphenodon. Palacrodon and Opisthias 

 are known only from mandibles. The former, however, is said to 

 have teeth quite like those of Ardeosaurus which, according to 

 Nopcsa, is a near relative of Acrosaurus. Nor is the temporal region 

 of Ardeosaurus as well known as one could wish. Brachyrhinodon 

 has two temporal arches, but is poorly known otherwise. Of Eifelo- 

 saurus the skull is wholly unknown. 



Middle and Upper Triassic. ? Eifelosaurus Jaekel, ? Polyspheno- 

 don Jaekel, Germany. Palacrodon Broom, South Africa. Brachy- 

 rhinodon Huene, Scotland. 



Upper Jurassic. Homceosaurus, v. Meyer, Ardeosaurus v. Meyer, 

 Germany.^ 



i[But cf. page 268 above. According to C. L. Camp (1923), Ardeosaurus is 

 related to the geckos. — Ed.] 



